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Related Party Transactions Disclosure of interests in subsidiaries (Details) | 1 Months Ended | 3 Months Ended | 4 Months Ended | 6 Months Ended | 11 Months Ended | 12 Months Ended
--- | --- | --- | --- | --- | --- | ---
Dec. 31, 2018 | Jul. 30, 2018 | Jun. 30, 2020 | Mar. 31, 2020 | Dec. 31, 2019 | Sep. 30, 2019 | Jun. 30, 2019 | Mar. 31, 2019 | Nov. 29, 2018 | Dec. 31, 2020 | Jun. 21, 2018 | Dec. 31, 2020
TransAlta Renewables Inc. |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of subsidiaries [line items] |  |  |  |  |  |  |  |  |  |  |  |
Ownership interest (as a percent) | 60.90% | 61.10% | 60.20% | 60.30% | 60.40% | 60.50% | 60.60% | 60.80% | 61.00% | 60.10% | 64.00% |
Canada | TransAlta Generation Partnership |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of subsidiaries [line items] |  |  |  |  |  |  |  |  |  |  |  |
Ownership interest (as a percent) |  |  |  |  |  |  |  |  |  |  |  | 100.00%
Canada | TransAlta Cogeneration, L.P. |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of subsidiaries [line items] |  |  |  |  |  |  |  |  |  |  |  |
Ownership interest (as a percent) |  |  |  |  |  |  |  |  |  |  |  | 50.01%
Canada | TransAlta Energy Marketing Corp. |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of subsidiaries [line items] |  |  |  |  |  |  |  |  |  |  |  |
Ownership interest (as a percent) |  |  |  |  |  |  |  |  |  |  |  | 100.00%
Canada | TransAlta Renewables Inc. |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of subsidiaries [line items] |  |  |  |  |  |  |  |  |  |  |  |
Ownership interest (as a percent) |  |  |  |  |  |  |  |  |  |  |  | 60.10%
US | SP Skookumchuck Investment, LLC |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of subsidiaries [line items] |  |  |  |  |  |  |  |  |  |  |  |
Proportion of ownership interest in joint venture |  |  |  |  |  |  |  |  |  |  |  | 49.00%
US | EMG International, LLC |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of subsidiaries [line items] |  |  |  |  |  |  |  |  |  |  |  |
Proportion of ownership interest in joint venture |  |  |  |  |  |  |  |  |  |  |  | 30.00%
US | TransAlta Centralia Generation, LLC |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of subsidiaries [line items] |  |  |  |  |  |  |  |  |  |  |  |
Ownership interest (as a percent) |  |  |  |  |  |  |  |  |  |  |  | 100.00%
US | TransAlta Energy Marketing (U.S.), Inc. |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of subsidiaries [line items] |  |  |  |  |  |  |  |  |  |  |  |
Ownership interest (as a percent) |  |  |  |  |  |  |  |  |  |  |  | 100.00%
Australia | TransAlta Energy (Australia), Pty Ltd. |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of subsidiaries [line items] |  |  |  |  |  |  |  |  |  |  |  |
Ownership interest (as a percent) |  |  |  |  |  |  |  |  |  |  |  | 100.00%

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- Definition The proportion of ownership interest in a joint venture attributable to the entity. [Refer: Joint ventures [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 27 -IssueDate 2019-01-01 -Paragraph 17 -Subparagraph b -Clause iii -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=27&code=ifrs-tx-2019-en-r&anchor=para_17_b_iii&doctype=Standard -URIDate 2019-03-27 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 27 -IssueDate 2019-01-01 -Paragraph 16 -Subparagraph b -Clause iii -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=27&code=ifrs-tx-2019-en-r&anchor=para_16_b_iii&doctype=Standard -URIDate 2019-03-27 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 12 -IssueDate 2019-01-01 -Paragraph 21 -Subparagraph a -Clause iv -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=12&code=ifrs-tx-2019-en-r&anchor=para_21_a_iv&doctype=Standard -URIDate 2019-03-27 + Details
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- Definition The proportion of ownership interest in a subsidiary attributable to the entity. [Refer: Subsidiaries [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 27 -IssueDate 2019-01-01 -Paragraph 17 -Subparagraph b -Clause iii -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=27&code=ifrs-tx-2019-en-r&anchor=para_17_b_iii&doctype=Standard -URIDate 2019-03-27 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 27 -IssueDate 2019-01-01 -Paragraph 16 -Subparagraph b -Clause iii -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=27&code=ifrs-tx-2019-en-r&anchor=para_16_b_iii&doctype=Standard -URIDate 2019-03-27 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 12 -IssueDate 2019-01-01 -Paragraph 19B -Subparagraph c -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=12&code=ifrs-tx-2019-en-r&anchor=para_19B_c&doctype=Standard -URIDate 2019-03-27 + Details
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